The 81st Annual Meeting of the American Association of Physical Anthropologists (2012)

Force of habit: dietary properties, masticatory function and cranial plasticity


1Biological Sciences, Aerospace and Mechanical Engineering, and Anthropology, University of Notre Dame, 2Mechanical and Aerospace Engineering, University of Missouri, 3Mechanical and Aerospace Engineering, University of Missouri

Friday 2:30-2:45, Galleria South Add to calendar

Dietary properties have a profound effect on craniofacial development, inducing a cascade of changes at the gross, tissue, cellular, protein and genetic levels. Indeed, diet-related variation in masticatory stresses is thought to result in tissue modeling and remodeling that maintains the structural integrity of the feeding complex. However, our knowledge of the hierarchical network of such plasticity responses is differentially limited to bony elements. Because jaw joints are composite structures comprised of hard and soft tissues, analysis of the nanoscale properties of joint cartilage may provide unique information regarding the mechanobiology of the masticatory system in growing organisms.

We investigated the plasticity of jaw-joint cartilage in three rabbit cohorts obtained as weanlings and raised on different diets until adult. To account for the viscoelastic or time-dependent behavior of biological tissues, maximum load (creep) and maximum displacement (relaxation) tests were performed on the cartilage with a spherical-tip indenter with 20-micron radius. The creep test was performed with a 500 ┬ÁN maximum load for 30 seconds, while the relaxation test occurred with a 3-micron maximum displacement for 30 seconds. The DMA (Dynamic Mechanical Analysis) test was used to obtain storage modulus and loss modulus.

Results indicate that long-term variation in masticatory forces related to dietary properties is associated with changes in nanoscale cartilage properties, which in turn underlies variation in jaw-joint biomechanics. This engineering approach offers novel insights into the functional bases of anatomical variation in joint formation, with myriad implications for understanding the evolution of the primate skull and feeding apparatus.

Supported by NSF grant BCS-0924592.

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